Fix big-endian codegen bug in DAGTypeLegalizer::ExpandRes_BITCAST

On PowerPC, a bitcast of <16 x i8> to i128 may run through a code
path in ExpandRes_BITCAST that attempts to do an intermediate
bitcast to a <4 x i32> vector, and then construct the Hi and Lo parts
of the resulting i128 by pairing up two of those i32 vector elements
each.  The code already recognizes that on a big-endian system, the
first two vector elements form the Hi part, and the final two vector
elements form the Lo part (vice-versa from the little-endian situation).

However, we also need to take endianness into account when forming each
of those separate pairs:  on a big-endian system, vector element 0 is
the *high* part of the pair making up the Hi part of the result, and
vector element 1 is the low part of the pair.  The code currently always
uses vector element 0 as the low part and vector element 1 as the high
part, as is appropriate for little-endian platforms only.

This patch fixes this by swapping the vector elements as they are
paired up as appropriate.

llvm-svn: 165802

2 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
index bb54fd24e21..6bcb3b25e98 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
@@ -124,6 +124,10 @@ void DAGTypeLegalizer::ExpandRes_BITCAST(SDNode *N, SDValue &Lo, SDValue &Hi) {
         // there are only two nodes left, i.e. Lo and Hi.
         SDValue LHS = Vals[Slot];
         SDValue RHS = Vals[Slot + 1];
+
+        if (TLI.isBigEndian())
+          std::swap(LHS, RHS);
+
         Vals.push_back(DAG.getNode(ISD::BUILD_PAIR, dl,
                                    EVT::getIntegerVT(
                                      *DAG.getContext(),
diff --git a/llvm/test/CodeGen/PowerPC/2012-10-12-bitcast.ll b/llvm/test/CodeGen/PowerPC/2012-10-12-bitcast.ll
new file mode 100644
index 00000000000..e7dc706a889
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/2012-10-12-bitcast.ll
@@ -0,0 +1,20 @@
+; RUN: llc < %s | FileCheck %s
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v128:128:128-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+define i32 @test(<16 x i8> %v) nounwind {
+entry:
+  %0 = bitcast <16 x i8> %v to i128
+  %1 = lshr i128 %0, 96
+  %2 = trunc i128 %1 to i32
+  ret i32 %2
+}
+
+; Verify that bitcast handles big-endian platforms correctly
+; by checking we load the result from the correct offset
+
+; CHECK: addi [[REGISTER:[0-9]+]], 1, -16
+; CHECK: stvx 2, 0, [[REGISTER]]
+; CHECK: lwz 3, -16(1)
+; CHECK: blr
+